Summary translation

The Potato Virus Y (PVY), transmitted non-persistently by winged morphs of many aphid species is a main problem in seed potato production. Short wave light reflecting material has been shown to reduce virus incidence by optically distracting virus vectors in many crops. Straw mulch is a suitable reflective material and contributed to significant reduction of virus infection in conventional potatoes and oil seed rape. In small scale organically managed field experiments carried out in Northern Hessen (4 replicates, cv. Christa, 0% PVY at planting), straw mulch and chitting were compared to an untreated control in 2000 for virus reduction potential. In 2001 and 2002, straw mulch and chitting were combined in a factorial experiment. To increase PVY inoculum center rows of all plots were planted with infector plants (85 % PVY in 2000, 100% in 2001 and 2002). PVY infection of tubers at harvest were tested with ELISA. Flight activity of alates was monitored with yellow water traps. Potato colonizing aphids were counted on 100 leaves per plot in weekly to fortnightly intervals. In all years mulching significantly reduced aphid infestation on leaves and PVY incidence. In 2000 chitting effects on PVY were not significant, whereas in 2001 and 2002 chitting reduced PVY incidence significantly. Marketable tuber yield was increased under straw mulch (not significant) and (in 2001, but not in 2002) by chitting. Straw mulch is probably most effective if vector pressure is high early in the year and the susceptibility of young potato plants is highest. In later growth stages its effect declines gradually according to progressing ground coverage of the crop. This is supported by the higher virus reduction efficiency of mulch in 2000, when aphid spring flight, measured in yellow water traps was substantially higher than in 2001.